1. Field of the Invention
This invention is directed to a grid for covering an opening and more particularly to a grid for covering an opening in which hollow tubes having cores therein are received in supports on opposite sides of the opening such that the ends of the cores are positioned within the support thereby preventing the cutting of the tube.
2. Description of the Prior Art
For a great number of years, grids for windows or other openings have been protected against willful destruction by sawing, by designing the grid bars as tubes with loose iron rods in them so that, on making any attempt at sawing, the rods are turned and not readily cut. Furthermore, such forms of grids have been used for protection of lighting shafts against thieves making an attempt at breaking into a building. In this case, the grid has under its normal grid bars, stretching across the lighting shaft, two U-girders which are fixed to the side walls of the shaft by screw-plugs let into the wall. Four-cornered iron blocks are welded to the U-girders for taking up steel pipes, flattened at their ends, and having within them round steel rods, cut to the desired length (see German Offenlegungsschrift specification No. 2,624,149). Such round steel rods placed loosely within the steel tubes necessarily have to be shorter than the steel tubes themselves in this design so that, in fact, the steel tubes may be cut through next to the iron blocks by a thief.